Synchronous motor



0a,.12, 1948. HAN EN Em 2,450,955

SYNCHRONOUS mo'ron Filed July 31, 1947 2 Sheets-Sheet 1 INVENTORSWILLIAM L. mwsm. mm M nuns-r,

ATTORNEYS Oct. 12, 1948.

w. L. HANSEN ETAL smcnnonous ub'ron Filed July 31, 1947 2 Sheet s-Sheet2 INVENOR 5 WILLIAM LHA EN. BY J M N-HURS T z I ATTORNEYS Patented Oct.12, 1948 2,450,955 SYNCHRONOUS MOTOR William L. Hansen and Ira N. Hurst,Princeton,

Ind.,

assignors to Hansen Mfg. Company,

Princeton, Ind., a corporation of Indiana Application July 31, 1947',Serial No. 765,110 6 Claims. (Cl. 172278) 1 This invention relates inparticular to electrical synchronous motors such as are employed foroperating clocks and for performing other small duty work.

In the type of motor to which this invention particularly applies, axialor outer pole pieces .are employed which surround the field coil.

These pole pieces form part of a magnetic field member which is mountedat one end on a core which receives the field coil. A second magnetic toelectric motors and field member is mounted on the other end of r thecore and is provided with inner or lateral pole pieces disposed radiallywith their tips spaced from the tips of the axial pole pieces to leave acontinuous annular opening between polein a central position withrespect to the axis 1 of the motor and has a plurality of openings aboutits periphery for snugly receiving the axial pole pieces, thereby toconstrain these members to a strictly concentric position with respectto the axis of the motor. The invention will be bet ter understood whenreference is made to the following description and the accompanyingdrawings in which:

Figure 1 represents a partial plan and a partial transverse sectionalview of a synchronous motor having axial pole pieces and to which thetips. A rotor is positioned within this annular opening. In order toprovide a rotating magnetic field, one set and preferably both sets ofpole pieces, are shaded by the use of undulating rings of non-magneticmetal. A motor of this general type is shown and described in the Hansenand Hurst Patents Nos. 2,256,711 and 2,298,373 patented September 23,1941, and October 13, 1942,

. respectively.

ture and assembly there is a tendency for one 4 or more of the polepieces to spring out of shape or position, particularly when the shadingring or rings are being applied. The result is that the annular gapbetween the pole tips may not be of uniform width throughout the entirelength of the gap and the operating eflicien-cy of the motor mighttherefore decrease due to the variation of the field throughout themagnetic path.

The general object of the invention is to provide a synchronous motor inwhich the annular interpole space is strictly of a pre-determined widththroughout its length so that the intensity of the magnetic field at thegap remains constant.

Another object is to provide an improved type of synchronous motor andmore particularly an improvement in the manufacture and assembly of themotor by which the cooperating pole pieces are maintained strictly inconcentric relation with respect to the central axis of the motor.

The above objects are attained, in brief, by providing a cup shapedelement which is fixed present invention applies. This view is taken atapproximately the position indicated by line 1-! in Fig. 3 but Fig. 1 isof smaller size than Fig. 3.

Figure 2 is a perspective view of a portion of an improved cup shapedmember or accessory which may be employed to hold the axial pole piecesstrictly in place.

Figure 3 is a vertical section, somewhat enlarged, of the motor shown inFig. 1 but mounted on a base and with the pole-locating accessory inposition.

Figure 4 represents a sectional view taken along line 4- in Fig. 3.

Referring to the drawings in detail, numeral i (Fig. 3) designates amagnetic tubular hub having reduced diameter portions 2, 3 and uponwhich are mounted the outer and inner field pole assemblies. The outerfield pole structure consists of a disc 4 having an aperture by which itis mounted on the reduced diameter portion 2 of the hub I and havingaxially directed pole pieces 5, 6 disposed alternatingly in acylindrical path around the hub i. The pole pieces 5, 6 are preferablynot equidistantly spaced about the disc 4 but instead are arranged inpairs around the periphery of the disc as can best be seen in Fig. 4.

The alternating pole pieces 5, 6 are shaded by an undulating ring l ofnonmagnetic material such as copper. This undulating ring passes overthe outer surfaces of the pole pieces 5 and therefore does not shadethem. The ring 1, however, is provided with undulating portions 8passing around three sides of the pole pieces 6 thereby shading thesepole pieces and providing a phase leg when the field structure ismagnetized by an alternating flux. v

The inner pole piece assembly consists .of a pair of discs 9, l2 havingapertures by which they are mounted on the reduced diameter portion 3 ofthe huh I. The discs are provided with pole pieces III, II respectivelywhich extend practically radi- "of the pole pieces.

3 ally from the discs and when assembled on top of one another, the polepieces I of one disc form a plurality of pairs of pole pieces with thepole pieces ll' of the other disc around the periphery of the assembleddiscs. The pole pieces III, II do not extend as far as the pole piecesI, but instead are cut short so as to leave an annular space between thetips of the pole pieces II, II and the inner peripheral surface of thepole pieces 5, 6; the width of this annular space is such as toaccommodate the thickness of a rotor. The disc i2 is spaced from theshoulder formed by the reduced diameter portion 8 by a cup shapedelement I I which will be described in detail hereinafter. this elementbeing mounted on portion 3 of the tubular hub.

The pole pieces l0 may be bent downwardly while the pole pieces H arebent upwardly so that their ends, looking toward the periphery, are insubstantially the same plane. An undulating ring H of non-magnetic metalsuch as copper is interposed between the discs 9, l2 at the positionThis shading ring has undulating portions passingaround three sides ofeach of the pole pieces I i so as to shade them. However, the ring l2merely passes across the front of the face of each pole piece l0 andtherefore does not shade it. As can be seen on the drawings, the shadingring has considerable width measured in the radial direction so that thepole pieces i0, II are likewise of considerable length in order toaccommodate the shading a The field structure formed by the radial polepieces l0, ii and the axial pole pieces 5, 6 is magnetized by a fieldcoil l5 wound on a drum ll of insulating material and contained betweena pair of insulating webs IT. The drum i6 is mounted on the hub I andsecured thereto in any suitable and well known manner. There are a pairof leads (not shown) connected to opposite ends of the coil and adaptedto be connected to a suitable source of alternating current. Themagnetic hub is provided with an axial bore l8 closed at each end by theplug washers l9 seated in recesses at the hub and abutting several innerwashers mounted at the ends of a sleeve 2|. The washers I! have anopening at the center for receiving the shaft 22 of a rotating disc 23made of a light metal such as aluminum and provided with a number ofequidistantly spaced large openings 24. The disc 23 is secured to theshaft 22 by means of a hub member 25 having a downwardly extendingcollar 26 which bears against the upper washer.l9. The space within thebore between the shaft and the inner washers 20and sleeve 2| may befilled with a liquid lubricant or with waste saturated with a lubricant.

The rotor band 21 is provided with circumferentially spaced incisions 28indicated in Fig. 1, preferably as many as there are pairs of poles andequidistantly spaced incisions serve to interrupt the magnetic path andin this manner to provide poles around the rotor band. The width of therotor band 2! should preferably be greater than the thickness of theradial or inner pole pieces Ni, ii as shown in Fig. 3. It should also benoted in this figure that the axial pole pieces I, I extend for a shortdistance beyond the upper surfaces of the radial pole pieces l0, Ii.

In the fabrication of the improved motor, the

4 causing the undulations l closely to embrace thewiderpolepiecestascanbeseeninl 'lg. 1. The next stepis to apply the discl2 to the hub I with the pole pieces ll bent upwardly and positionedangularly with respect to the axial pole pieces. Theshadingringllisthenplacedoverthedisc I2 and rotated slightly to cause the polepieces it to fit into the undulations of the ring. l'inally,thedisciisplacedovertheshadingring I with the pole piecesextending downwardly so as to fit snugly into the downwardly extendingundulations of the ring ll. Assuming that the pole pieces I! have beenproperly positioned with respect to the pole pieces I, I, the polepieces II will automatically take the position shown in Fig. 1 withrespect to the axial pole pieces. The field circuit is then complete.

It has been found that when the shading ring'lisbeingappliedtothepolepieceslJthereisa tendency to bend inwardly,even though slightly. any one or more of the axial pole pieces I, 6.ObviousU, the leverage applied to the upper ends of the pole pieces 8, 6about the positions where it joins the disc 4 is considerable so that itmay .not require much force to bend the axial pole pieces slightly outof cylindrical alignment. The

direct effect is to vary the width of the annular space between a pairof pole pieces II, II and its immediately adjacent pair I, O and themagnetic flux moving from one pair of pole pieces to the other andintercepted by the rotor band 2! obviously varies. This variation influx in the travel path of the rotor tends to introduce variations inthe rotary efl'crt of the rotor and in an exaggerated case, as when anaxial pole piece is bent considerably inward, the resulting friction onthe rotor may be suilicient to prevent rotation.

This invention has for its main object the maintenance of the properposition of these axial pole pieces during manufacture and assembly offirst step is to mount the coil IS on the hub after 7 the motor andthroughout the operating life. For this purpose and as shown in Figs. 2.3 and 4, I employ a cup shaped member II which has the central openingtightly fitted about the portion 3 of the tubular hub i. Non-magneticmaterial such as fiber, specially treated cardboard. thermosettingplastic or any other material that lends itself to a pressing operationand rigidly retains its shape even under slight amount of heat, may beused. Non-magnetic metal such as aluminum and copper may also be usedfor this purpose although we prefer to employ non-metal materials tominimize cost. The member is provided with a base portion indicated at2! and a downwardly extending flange portion 20 which merges into a flatperipheral portion 2]. The latter is also formed at its outer extremitywith a fairly deep flange 22. A plurality of large holes indicated at 33may be provided in the base portion 2| to reduce weight and a series ofopenings 24 may be provided in the flat portion ll for snugly receivingeach pair of the axial pole pieces 5, 6. These openings are of anannular slot-like character and each opening is adapted to receive onepair of the axial pole pieces.

The cup shaped member I! is applied to the tubular element I directly ontop of the upper web i! before the disc i2 and shading ring I 4 areplaced in position. It is therefore a simple matter to cause the axialpole pieces I, I to enter the openings 34 and then by pressing themember I! still downwardly, the central opening in the member can beforced over portion 3 of the tubular element. Thus the axial pole piecesare held rigidly in position by this cup shaped element II and theannular shape between said sequent manufacturing or assembly operationson the motor. Due to the end positions that the pole-pieces assume,within the slots, no outward movement of the pole pieces is possible. Ifdesired, separate slots for employed \which would idly in fourdirections.

place, the two pole piece discs 7 ing ring N can be applied to thetubular member I, and if desired, the metal of the discs peened to thehub to hold the parts together.

In order further to offer protection to the pole pieces and the workingparts of the motor, we may provide a non-magnetic shield 35 of anysuitable shape to fit snugly over the outside periphery of the member[3, also over the upper edge of the pole pieces 5, 6 and in additionover the entire upper surfaceof the rotor. In order to adapt the motorto a clock mechanism, the lower portion 2 of the huh I may be receivedin, an opening 36 of a metal case 31 which ,contains gearing of anysuitable type which is connected through a pinion (not shown) affixed tothe With the member l3 in shaft 22.

From the foregoing it is evident that we have provided an accessory inthe form of a cupshaped member l3 which strictly locates the axial polepieces 5, 6 in the vertical direction due to of the openings 34, andtheir predetermined distance from the center of the motor. In addition,the end surfaces of the openings 34 position these pole pieces in theendwise direction to assure that the pole pieces of each pair will notmove outwardly with respect to one another. Thus the axial pole piecesare maintained rigidly in position withstanding any tendency to move thesame when the shading ring] is mounted on the pole pieces or any otherforce is acting to distant the pole pieces from their correct position.

The latter, together with the radial pole pieces l0, II, are thereforecaused to be spaced a predetermined distance apart so that the rotorelement 2.1 will be subjected to the same flux intensity throughout itstravel in the inter-pole annular space. The use of the pole-retainingmember l3 does not greatly increase the cost of the motor since thismember can be cheaply made on standard presses and no special provisionis necessary to hold the member in axial position because the polepieces I0, I I bear against'the member l3 and are peened to the hub.

Having thus fully described our invention what we claim as new anddesire to secure by Letters Patent is:

1. In a synchronous motor, a magnetic core, a coil surrounding saidcore, a magnetic field member mounted on one end of said core and havingouter pole pieces disposed axially in a substam tiaily cylindrical path,a second magnetic field member mounted on the other end of said core andhaving inner pole pieces disposed radially with their tips spacedfromthe tips of the axial pole pieces to leave a continuous annularopening between the pole tips, a rotor positioned within said-annularopening, and a shading ring positioned adjacent to and intertwining saidouter pole pieces and arranged to shade alternate outer pole pieces, andmeansmounted on said core second magnetic field member and said coil formaintaining said outer pole pieces rigidly in position with respect tothe inner pole pieces,

each pole piece may be hold these elements rigl2, 9 and the shadmay be2. In a. synchronous motor, a magnetic core,- a coil surrounding saidcore. a magnetic field member mounted on one end of said core and havingouter pole pieces disposed axially in a substantially cylindrical path,a second magnetic field member mounted on the other end of said core andhaving inner pole pieces disposed radially with their tipsspaced fromthe tips of the axial pole pieces to leave a continuous annular openingbetween the pole tips, a rotor posi-' tioned within said annularopening, and a shading ring positioned adjacent to and intertwining saidouter pole pieces and arranged to shade alternate pole pieces, and meansmounted on said core between said second magnetic field member and saidcore for constraining the outer pole pieces to said cylindrical path,the central axis of which coincides with the axis of the motor.

3. In a, synchronous motor, a magnetic core, a magnetic field membermounted on one end of said core and having outer pole pieces disposedaxially in a substantially cylindrical path, a second magnetic fieldmember mounted on the other end of said core and having inner polepieces disposed radially with their tips spaced from the tips of theaxial pole pieces to leave a continuous annular opening between the poletips, a rotor positioned within said annular opening, and a shading ringpositioned adjacent to and intertwining said outer pole pieces andarranged to shade alternate outer pole pieces, said means comprising acup shaped member which fits about the central core of the motor and isprovided with openings for snugly receiving said axial pole pieces.

4, In a synchronous motor, a magnetic core, a coil surrounding saidcore, a magnetic field member mounted on one end of said core and havingouter pole pieces disposed axially in a substantially cylindrical path,said pole pieces being arranged in pairs with a greater annular distancebetween pairs than between the pole pieces of each pair, a secondmagnetic field member mounted on the other end of said core and havinginner pole pieces disposed radially with their tips spaced from the tipsof the axial pole pieces to leave a continuous annular opening betweenthe pole tips, said inner pole pieces being arranged in pairs with agreater annular distance between pairs than between the pole pieces ofeach pair, a rotor positioned in said annular opening, means forproducing a magnetic field in said field members, and means carried onsaid core interposed between said second magnetic field member and saidcell for maintaining the outer pole pieces in circular alignment withone another in order that the annular opening between pole tips shallbe-of uniform size throughout its entire length. r

5. In a synchronous motor,- a magnetic core, a magnetic field membermounted on one end of the core and having a fiat portion which extendsradially from the core and terminates in a plurality of outer polepieces extending at right angles to said flat portion, said outer polepieces being disposed axially in a substantially cylindrical path aboutsaid core, a second magnetic field member mounted on the other end ofsaid core and including a fiat portion which terminates in a pluralityof inner pole pieces extending radially from said. core but stoppingshort of said outer pole pieces so as to leave a continuous annularpieces extending radially fiat portions or said magnetic field members,and means for maintaining the outer pole pieces rigidly in position withrespect to the inner pole pieces, said means comprising a cup shapedmember which is interposed between one or the fiat surfaces or saidmagnetic field members and one end of the coil, said cup shaped memberbeing provided with a plurality of openings arranged in predeterminedpositions for snugly receiving the outer pole pieces and therebyrestraining any movement oi. these pole pieces away from the saidcylindrical path.

6. In a synchronous motor, a magnetic core, a magnetic field membermounted at one end 01' said core and having a fiat portion extendingradially from said core and terminating in a plurality of outer polepieces which are bent approximately 90 from said flat portion-and arearranged in a substantially cylindrical formation, a second magneticfield member mounted on the other end of said core and having a fiatportion which terminates in a plurality of inner pole from the core butstopping short of said outer pole pieces to leave a continuous annularopening between pole tips, a rotor positioned within said annularopening, a

shade alternate outer pole pieces,

positioned be- 8 tween the fiat surfaces of said magnetic field members,and means for maintaining said outer pole pieces rigidly in positionwith respect to the inner pole pieces, said means including a cup shapedmember positioned between one or said fiat surfaces oi the magneticfield members and said coil, said cup shaped member having a pluralityoi openings for snugly receiving the outer pole pieces to hold themwithin said cylindrical path, said cup shaped member also having aflange which fits snugly about outer portions of said shading ring.

WILLIAM Lfmmsms. IRA N. BURST.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,049,261 Haydon July 28, 19362,080,371 Hammond May 11, 1937 2,256,711 Hansen et al. Sept. 23, 19412,298,373 Hansen et a1 Oct. 13, 1942 2,424,020 Chatelain July 15, 1947FOREIGN PATENTS Number Country Date Great Britain Jan. 3, 1938

